Utils: Make a FilePath's osType publicly accessible

Will help with proper is{Relative,Absolute}Path implementations.

Change-Id: Icad90b5a55d9cf733f6ee66dbbe273ec9682d387
Reviewed-by: David Schulz <david.schulz@qt.io>

src/libs/utils/fileutils.h

@@ -174,6 +174,7 @@ public:
     bool isNewerThan(const QDateTime &timeStamp) const;
     QDateTime lastModified() const;
     QFile::Permissions permissions() const;
+    OsType osType() const;
     bool removeFile() const;
     bool removeRecursively(QString *error = nullptr) const;
     bool copyFile(const FilePath &target) const;